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(1 - 8 of 8)
- Title
- FACE/CORE DISBONDING FRACTURE OF HONEYCOMB CORE SANDWICH PANELS.
- Creator
- Tauhiduzzaman, Mohammad, Carlsson, Leif A., Florida Atlantic University, Department of Ocean and Mechanical Engineering, College of Engineering and Computer Science
- Abstract/Description
-
The objective of the research presented in this thesis is to develop analysis and test procedures for the characterization of disbonding crack growth in a honeycomb (HC) core sandwich structure. Face sheet-to-core disbonding are of particular interest to aircraft certification authorities due to several in-service occurrences. Experimental investigation was initially focused on the mode I dominated Single Cantilever Beam (SCB) test method. Various data reduction methodologies were employed to...
Show moreThe objective of the research presented in this thesis is to develop analysis and test procedures for the characterization of disbonding crack growth in a honeycomb (HC) core sandwich structure. Face sheet-to-core disbonding are of particular interest to aircraft certification authorities due to several in-service occurrences. Experimental investigation was initially focused on the mode I dominated Single Cantilever Beam (SCB) test method. Various data reduction methodologies were employed to determine the fracture toughness. The MBT method produced the most consistent and conservative results. Finite element analysis (FEA) a double periodic array of hexagonal cells was conducted to determine the effective in-plane extensional modulus and Poisson ratio of the HC core. It was shown that deformation constraints on the core, due to attachment of the core to rigid face sheets, will drastically change the behavior of the HC core. The response changes from being governed by bending to stretching which substantially elevates the effective in-plane modulus. Fracture mechanics analysis of a face/core interface crack in a HC core SCB specimen was performed using FEA. The influence of in-plane properties of the constrained core on energy release rate and mode mixity phase angle was examined. Use of plane strain conditions and an elevated modulus of the constrained core in the analysis is recommended. The approach is substantiated by testing of HC core SCB sandwich. Test results showed good agreement with FEA prediction of compliance and kink angle.
Show less - Date Issued
- 2019
- PURL
- http://purl.flvc.org/fau/fd/FA00013419
- Subject Headings
- Honeycomb structures, Fracture mechanics, Strength of materials, Airframes--Materials
- Format
- Document (PDF)
- Title
- Mode I interlaminar fracture toughness of interleaved graphite/epoxy.
- Creator
- Ozdil, Feridun., Florida Atlantic University, Carlsson, Leif A., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
Mode I interlaminar fracture toughness, G IC, of interleaved graphite/epoxy has been investigated with DCB specimens, beam theory, and finite element analysis. Finite element modeling aimed to investigate the influence of interleaf thickness on compliance and energy release rate and possible mixed mode loading in the case of asymmetric interfacial crack. Another objective was to compute crack tip yield zone dimensions as a function of thickness and elastic properties of the interleaf material...
Show moreMode I interlaminar fracture toughness, G IC, of interleaved graphite/epoxy has been investigated with DCB specimens, beam theory, and finite element analysis. Finite element modeling aimed to investigate the influence of interleaf thickness on compliance and energy release rate and possible mixed mode loading in the case of asymmetric interfacial crack. Another objective was to compute crack tip yield zone dimensions as a function of thickness and elastic properties of the interleaf material. The analysis is correlated with experiments. Thermoplastic interleaves enhanced G IC to a great extent. The toughness increased sharply with film thickness to a maximum at 16 mu m and decreased for the thicker interleaves. On the other hand, inadequate adhesion preempted the toughness potential of thermoset interleaves.
Show less - Date Issued
- 1991
- PURL
- http://purl.flvc.org/fcla/dt/14682
- Subject Headings
- Laminated materials--Testing, Fracture mechanics, Strength of materials
- Format
- Document (PDF)
- Title
- Strength and Modulus of Recycled Aggregate Concrete Subjected to Wetting and Drying Cycles.
- Creator
- Alawadi, Farah, Sobhan, Khaled, Florida Atlantic University, College of Engineering and Computer Science, Department of Civil, Environmental and Geomatics Engineering
- Abstract/Description
-
The reuse of crushed aggregates for producing structural concrete is a major concern especially when it comes to its strength and durability. This study evaluated recycled aggregate concrete (RAC) for its strength and durability under simulated environmental degradation in the form of wetting-drying (W-D) cycles. The study consisted of two phases, each involving the determination of the compressive strength and modulus of elasticity using the conventional method and also a nondestructive...
Show moreThe reuse of crushed aggregates for producing structural concrete is a major concern especially when it comes to its strength and durability. This study evaluated recycled aggregate concrete (RAC) for its strength and durability under simulated environmental degradation in the form of wetting-drying (W-D) cycles. The study consisted of two phases, each involving the determination of the compressive strength and modulus of elasticity using the conventional method and also a nondestructive ultrasonic pulse velocity method (Pundit Lab). Phase 1 involved 7-day curing followed by 30 W-D cycles, while Phase 2 included 28-day cured samples subjected to 15 W-D cycles. It was found that RAC specimens subjected to W-D cycles had minimal degradation in strength, making the use of RAC in construction very promising. Results from Pundit Lab compared reasonably well with conventional test results, showing promise as a nondestructive tool for the evaluation of RAC properties.
Show less - Date Issued
- 2018
- PURL
- http://purl.flvc.org/fau/fd/FA00013162
- Subject Headings
- Concrete, Durability of concrete, Strength of materials, Recycled aggregate concrete
- Format
- Document (PDF)
- Title
- Interlaminar mode III fracture ECT method - testing and analysis.
- Creator
- Browning, Grant., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
In an effort to obtain an improved mode III fracture toughness test suitable for a testing standard, mechanics analysis, experimental testing, and finite element analysis (FEA) have been conducted. Of particular concern are the merits of one-point and two-point edge crack torsion (ECT) test methods, the influence of specimen geometry that overhangs beyond load/support points, and the influence of crack length on the compliance and energy release rate. Shear stress distributions at the crack...
Show moreIn an effort to obtain an improved mode III fracture toughness test suitable for a testing standard, mechanics analysis, experimental testing, and finite element analysis (FEA) have been conducted. Of particular concern are the merits of one-point and two-point edge crack torsion (ECT) test methods, the influence of specimen geometry that overhangs beyond load/support points, and the influence of crack length on the compliance and energy release rate. Shear stress distributions at the crack front are determined to examine the uniformity of mode III loading and mode II influence. The shear stress distributions in the one-point and two-point tests are virtually identical, indicating that either of the two tests could be used interchangeably. Based on the uniformity of the mode III shear stress distribution along the crack front, it was found that the ECT specimen should have minimum overhang. Longer crack lengths tend to produce nonuniform shear stress distributions. A modified two-point ECT test fixture was developed to allow testing of specimens with a range of dimensions. This development enabled experimental verification of the results from the FEA overhang series. The specimens with a minimum overhang produced consistant mode III toughness data. The most reliable way to reduce data is through the original compliance calibration method. A modified ECT specimen was developed with a staggered crack front to produce uniform mode III crack growth. Finite element analysis of the modified ECT specimen shows a uniform mode III stress distribution along the crack front with little mode II interaction.
Show less - Date Issued
- 2009
- PURL
- http://purl.flvc.org/FAU/187206
- Subject Headings
- Laminated materials, Testing, Fracture mechanics, Strength of materials, Testing, Composite materials, Testing
- Format
- Document (PDF)
- Title
- Silicone (RTV) sealant bonded aluminum joints: An experimental study.
- Creator
- Antony, Melvin., Florida Atlantic University, Hartt, William H.
- Abstract/Description
-
The performance of adhesively bonded joints in terms of strength, sealing capacity and environmental resistance is of concern to designers in many fields including the marine industry. In the present work floating roller peel tests were utilized to study the bond properties of aluminum-silicone (RTV) joints. An attempt was made to identify the factors that affect the joint strength. Experiments revealed that peel strength increased with sealant thickness and decreased at high peel rates....
Show moreThe performance of adhesively bonded joints in terms of strength, sealing capacity and environmental resistance is of concern to designers in many fields including the marine industry. In the present work floating roller peel tests were utilized to study the bond properties of aluminum-silicone (RTV) joints. An attempt was made to identify the factors that affect the joint strength. Experiments revealed that peel strength increased with sealant thickness and decreased at high peel rates. Organo-silane primer SS4044 was found to improve the weatherability and strength of the joint. Results point out that mechanical interlocking combined with chemical alteration of the substrate surface was responsible for this improved adhesion. Combinations of three different environmental parameters were studied, and it was shown that seawater was the most hostile single type and a combined exposure to seawater and UV radiation (to simulate a marine environment) proved to be the worst overall. Tests showed that relaxation was governed by sealant thickness alone and was not affected by the marine environment.
Show less - Date Issued
- 1991
- PURL
- http://purl.flvc.org/fcla/dt/14711
- Subject Headings
- Aluminum--Bonding, Sealing compounds, Strength of materials
- Format
- Document (PDF)
- Title
- Centrally prestressed fiber reinforced concrete columns.
- Creator
- Grijalba, Daniel A., College of Engineering and Computer Science, Department of Civil, Environmental and Geomatics Engineering
- Abstract/Description
-
With the need to improve corrosion resistance in columns and piles, the innovative idea of Centrally Prestressed Fiber Reinforced Concrete (CPFRC) columns is a promising solution. The first step is to compare if the compressive strength of any mix is affected by the size, geometry, or even the inclusion of polyolefin fibers in a specimen. The results showed that the cylinder size of 4 in. x 8 in., which is the most common size used by the testing labs, has the highest compressive strength....
Show moreWith the need to improve corrosion resistance in columns and piles, the innovative idea of Centrally Prestressed Fiber Reinforced Concrete (CPFRC) columns is a promising solution. The first step is to compare if the compressive strength of any mix is affected by the size, geometry, or even the inclusion of polyolefin fibers in a specimen. The results showed that the cylinder size of 4 in. x 8 in., which is the most common size used by the testing labs, has the highest compressive strength. There was no sign on compressive strength improvement with the use of polyolefin fibers, except for reduction in cracking size and concrete spalling. The second step compared the ultimate strength, ductility characteristics and failure mode of CPFRC columns to conventional columns. CPFRC showed adequate axial and flexural resistance, in addition to ductile behavior similar to regular reinforced concrete columns.
Show less - Date Issued
- 2011
- PURL
- http://purl.flvc.org/FAU/3332253
- Subject Headings
- Prestressed concrete construction, Strength of materials, Composite reinforced concrete, Concrete, Chemical resistance
- Format
- Document (PDF)
- Title
- Evaluation of the structural applicability of centrally prestressed, unreinforced concrete (CPUC) columns with modified Freyssinet hinges for marine and seismic environment.
- Creator
- Periyaiah, Rathinam., Florida Atlantic University, Reddy, Dronnadula V., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
An innovative concept of the Centrally Prestressed, Unreinforced Concrete (CPUC) column with modified Freyssinet hinges formulated by Paul Csagoly, to prevent rebar corrosion and additionally mitigate seismic damage, was investigated. The first phase of this work emphasized the mode of failure, ultimate strength, and ductility characteristics of the CPUC columns. As expected, CPUC columns showed adequate axial and flexural resistance as well as ductility. The ultimate strengths of most of the...
Show moreAn innovative concept of the Centrally Prestressed, Unreinforced Concrete (CPUC) column with modified Freyssinet hinges formulated by Paul Csagoly, to prevent rebar corrosion and additionally mitigate seismic damage, was investigated. The first phase of this work emphasized the mode of failure, ultimate strength, and ductility characteristics of the CPUC columns. As expected, CPUC columns showed adequate axial and flexural resistance as well as ductility. The ultimate strengths of most of the CPUC columns were about 10 to 20% higher than those of conventional ones. The second phase dealt with an energy absorbing device compatible with CPUC column to meet the occasional high ductility demand of the CPUC columns in earthquake conditions. Hinges were tested for compressive strength and moment-rotation capability. Parametric studies of the hinges were conducted for different filler materials, and width-to-height ratios. The confined filler material in the Freyssinet type hinge was found to have excellent compressive strength and moment-rotation capability. The parameters, width-to-height ratios and different filler material, had significant effect on hinge's performance.
Show less - Date Issued
- 1996
- PURL
- http://purl.flvc.org/fcla/dt/15253
- Subject Headings
- Columns, Concrete--Testing, Prestressed concrete construction--Testing, Strength of materials
- Format
- Document (PDF)
- Title
- Local buckling and debond propagation in sandwich columns and panels.
- Creator
- Aviles, Francis., Florida Atlantic University, Carlsson, Leif A., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
The local buckling failure mechanism and subsequent debond propagation in sandwich columns and panels with composite face sheets containing a face-to-core debond is experimentally, analytically, and numerically analyzed. The experimental investigation is based on a comprehensive test program to examine local buckling failure and fracture toughness of sandwich specimens consisting of glass/epoxy face sheets over various density PVC foams and a balsa wood core. Elastic foundation and finite...
Show moreThe local buckling failure mechanism and subsequent debond propagation in sandwich columns and panels with composite face sheets containing a face-to-core debond is experimentally, analytically, and numerically analyzed. The experimental investigation is based on a comprehensive test program to examine local buckling failure and fracture toughness of sandwich specimens consisting of glass/epoxy face sheets over various density PVC foams and a balsa wood core. Elastic foundation and finite element models are developed for prediction of the local buckling load of sandwich columns and panels containing an implanted debond at the face/core interface. Nonlinear finite element analysis was conducted to investigate debond propagation in the post-buckling region. Overall, model predictions were in agreement with experimental results. The buckling load was found to decrease with reduced face sheet stiffness, reduced core modulus, and increased debond length. Sandwich panels with circular debonds were more resistant to local buckling than those with square debonds of the same characteristic size. Circular debonds of 50 mm diameter and square debonds of 45 mm side length established the threshold for local buckling failure. Nonlinear finite element analysis of debonded sandwich columns and panels showed that the major crack displacement is opening (mode I). The tendency of the crack tip to first open and then close after buckling of the face sheet is believed to be due to the formation of an eccentric load path at the onset of buckling. The fracture mechanics analysis of debonded sandwich panels showed that the energy release rate is much higher in the direction perpendicular to the applied load than along the loading direction, and exceeds the measured toughness value in the transverse direction. This explains the experimental observation that a debond embedded in a sandwich panel tends to propagate in the transverse direction.
Show less - Date Issued
- 2005
- PURL
- http://purl.flvc.org/fau/fd/FADT12123
- Subject Headings
- Buckling (Mechanics), Sandwich construction, Fracture mechanics, Diffusion bonding (Metals), Strength of materials
- Format
- Document (PDF)
